Orthopedics

Feature Article 

Longer Operative Time Is Associated With Increased Adverse Events After Anterior Cervical Diskectomy and Fusion: 15-Minute Intervals Matter

Nathaniel T. Ondeck, BS; Daniel D. Bohl, MD, MPH; Ryan P. McLynn, BS; Jonathan J. Cui, BS; Patawut Bovonratwet, BS; Kern Singh, MD; Jonathan N. Grauer, MD

Abstract

Little is known about the impact of operative time, as an independent and interval variable, on general health perioperative outcomes following anterior cervical diskectomy and fusion. Therefore, patients undergoing a 1-level anterior cervical diskectomy and fusion were identified in the American College of Surgeons National Surgical Quality Improvement Program. Operative time (as an interval variable) was tested for association with perioperative outcomes using a multivariate regression that was adjusted for differences in baseline characteristics. A total of 15,241 patients were included. Increased surgical duration was consistently correlated with a rise in any adverse event postoperatively, with each additional 15 minutes of operating time raising the risk for having any adverse event by an average of 10% (99.64% confidence interval, 3%–17%, P<.001). In fact, 15-minute increases in surgical duration were associated with incremental increases in the rates of venous thromboembolism, sepsis, unplanned intubation, extended length of hospital stay, and hospital readmission. Greater operative time, despite controlling for other patient variables, increases the risk for overall postoperative adverse events and multiple individual adverse outcomes. This increased risk may be attributed to anesthetic effects, physiologic stresses, and surgical site issues. Although it is difficult to fully isolate operative time as an independent variable because it may be closely related to the complexity of the surgical pathology being addressed, the current study suggests that surgeons should maximize operative efficiency as possible (potentially using strategies that have been shown to improve operative time in the 15-minute magnitude), without compromising the technical components of the procedure. [Orthopedics. 201x; xx(x):xx–xx.]

Abstract

Little is known about the impact of operative time, as an independent and interval variable, on general health perioperative outcomes following anterior cervical diskectomy and fusion. Therefore, patients undergoing a 1-level anterior cervical diskectomy and fusion were identified in the American College of Surgeons National Surgical Quality Improvement Program. Operative time (as an interval variable) was tested for association with perioperative outcomes using a multivariate regression that was adjusted for differences in baseline characteristics. A total of 15,241 patients were included. Increased surgical duration was consistently correlated with a rise in any adverse event postoperatively, with each additional 15 minutes of operating time raising the risk for having any adverse event by an average of 10% (99.64% confidence interval, 3%–17%, P<.001). In fact, 15-minute increases in surgical duration were associated with incremental increases in the rates of venous thromboembolism, sepsis, unplanned intubation, extended length of hospital stay, and hospital readmission. Greater operative time, despite controlling for other patient variables, increases the risk for overall postoperative adverse events and multiple individual adverse outcomes. This increased risk may be attributed to anesthetic effects, physiologic stresses, and surgical site issues. Although it is difficult to fully isolate operative time as an independent variable because it may be closely related to the complexity of the surgical pathology being addressed, the current study suggests that surgeons should maximize operative efficiency as possible (potentially using strategies that have been shown to improve operative time in the 15-minute magnitude), without compromising the technical components of the procedure. [Orthopedics. 201x; xx(x):xx–xx.]

Anterior cervical diskectomy and fusion (ACDF) is a common option for treating cervical disk disease.1,2 Indeed, the number of ACDF procedures performed each year has increased since 1990.1–3 The increase in the number of procedures has been accompanied by an increase in average patient age and average number of medical comorbidities.1–3 Given the growing prevalence of this procedure, as well as the increasingly complicated patient population, it is more important than ever to understand and minimize the risk of postoperative adverse events.

Surgical duration is an often-studied risk factor for complications following surgical procedures. It has been shown to be independently associated with adverse events in a variety of settings, including cardiac surgery, neurosurgery, bariatric surgery, and urological procedures.4–8 Orthopedic surgeons have also shown interest in this potentially modifiable risk factor, with studies mentioning its association with adverse events involving posterior spinal fusion, knee arthroplasty, calcaneus fracture repairs, and tibial plateau fracture repairs.9–12

Although ACDF studies involving adverse events have noted that increased operative time (as a binary variable) is associated with the total rate of adverse events, they have not attempted to quantify the increased risk associated with greater operative duration across the spectrum of operative times or been specific about which postoperative events are increased.13,14

The purpose of this study was to test for relationships between operative time (as an interval variable) and specific general health postoperative adverse events among patients undergoing ACDF. The analysis was restricted to 1-level procedures and employed appropriate multivariate adjustment to limit the extent that observed associations were due to confounding by baseline or procedural characteristics.

Materials and Methods

Study Population

This study was granted an exemption from review by the authors' institutional review board. A retrospective cohort study was conducted using the American College of Surgeons National Surgical Quality Improvement Program (NSQIP). The NSQIP is a national surgical safety and data-monitoring program that prospectively identifies patients undergoing major surgical procedures at more than 500 institutions nationwide. The program characterizes patients' baseline characteristics and then follows patients for the development of complications during the 30 days after surgery, regardless of discharge status. The NSQIP data undergo regular and rigorous quality audits and have been shown to have a combined disagreement rate of approximately 2% across all audits.15 The NSQIP has been used extensively in orthopedic research.10,12–14,16,17

Patients undergoing ACDF during 2005 to 2015 as part of the NSQIP were identified using Current Procedural Terminology codes 22551, 22554, and 63075. Multilevel procedures and cervical corpectomies were excluded by eliminating cases that contained the secondary Current Procedural Terminology codes 22552 or 63076 and 63081 or 63082, respectively. Additionally, patients undergoing auto-graft harvest via a separate incision were removed by eliminating cases with the secondary Current Procedural Terminology code 20937. Finally, patients with diagnosis codes for traumatic, oncologic, or infectious indications were also excluded.

Patient Characteristics

In terms of baseline characteristics, the NSQIP includes patient demographics such as age and sex. Height and weight information was used to calculate body mass index. Comorbidities, including diabetes, congestive heart failure, dyspnea on exertion, hypertension, end-stage renal disease, chronic obstructive pulmonary disease, smoking status, and anemia, were identified. Functional status was classified as independent vs dependent. American Society of Anesthesiologists classes 1 to 4 were used. Specific information regarding variable definitions is listed in the NSQIP materials.15

Regarding the independent variable, operative time was defined as time of incision to time of closure. This was available as a continuous variable (in minutes) in the NSQIP data set. Operative time (in minutes) was divided by 15 such that the risk associated with a 15-minute increase in operative time could be directly reported.

Adverse event information collected by the NSQIP and used for this study included mortality, myocardial infarction, anemia requiring transfusion, unplanned intubation, pneumonia, urinary tract infection, surgical site infection (including superficial, deep, and organ/space), sepsis (including systemic sepsis and septic shock), wound dehiscence, and venous thromboembolism (including deep venous thrombosis and pulmonary embolism). These groupings have been used previously in the NSQIP orthopedic literature.18,19 In addition, studied hospital metrics included hospital length of stay and hospital readmission.15 Length of stay was dichotomized as normal or extended, with extended hospital length of stay being defined as greater than the 75th percentile length of stay (>1 day).

Statistical Analysis

Statistical analyses were conducted using Stata version 13.1 software (Stata Corp LLP, College Station, Texas). Multivariate regression was employed so that associations could be reported as the increased risk associated with an increase in surgical duration.

Each regression model had the binary complication or hospital metric as the outcome variable, a primary predictor variable of operative time (in minutes) divided by 15-minute intervals, and control variables, including age, sex, body mass index, and the presence/absence of diabetes, congestive heart failure, dyspnea on exertion, hypertension, end-stage renal disease, chronic obstructive pulmonary disease, smoking status, and anemia. The regression technique used was Poisson regression with robust error variance, an alternative to log-binomial regression that enables direct estimation of relative risk in cohort studies.20

Because multiple statistical comparisons were conducted in this study, a Bonferroni correction was employed to set the level of significance at P<.0036.

Results

A total of 15,241 patients met inclusion criteria. The demographics of this population are presented in Table 1. The average operative time (±SD) was 100.2 minutes (±39.3 minutes). Figure 1 is a histogram of operative times.

Patient Demographics

Table 1:

Patient Demographics

Histogram of operative times.

Figure 1:

Histogram of operative times.

The overall rates of each adverse event and adverse hospital metric are presented in Table 2. Nearly 2% of patients experienced an adverse event. Of note, 21 (31.82%) of the 66 patients experiencing a surgical site infection required a reoperation. Figure 2 shows a trend of rising rates of occurrence of any adverse event (Figure 2A), extended hospital stay (Figure 2B), and readmission (Figure 2C) with 15-minute increases in surgical duration. For all 3 adverse outcomes, increases in rates were observed with nearly all 15-minute intervals across the studied operative times.

Adverse Event and Hospital Metric Rates (N=15,241)

Table 2:

Adverse Event and Hospital Metric Rates (N=15,241)

Rates of occurrence of any adverse event (A), extended hospital stay (B), and readmission (C), for 15-minute intervals.

Figure 2:

Rates of occurrence of any adverse event (A), extended hospital stay (B), and readmission (C), for 15-minute intervals.

Following adjustment for demographic and comorbidity characteristics, an increase in the operative time by 15-minute intervals was associated with an increase in the risk for the occurrence of “any adverse event” by 10% (99.64% confidence interval, 3%–17%, P<.001; Table 3). More specifically, each 15-minute increase in surgical duration was associated with an increase in the risk for venous thromboembolism by 19% (99.64% confidence interval, 4%–37%, P<.001), sepsis by 44% (99.64% confidence interval, 3%–103%, P=.002), and unplanned intubation by 17% (99.64% confidence interval, 3%–33%, P<.001; Table 3).

Impact of Operative Time on Risk for Adverse Outcomes

Table 3:

Impact of Operative Time on Risk for Adverse Outcomes

On analysis of the hospital metrics, each 15-minute increase in surgical duration was associated with an increase in the risk for extended hospital stay by 14% (99.64% confidence interval, 12%–16%, P<.001) and risk for hospital readmission by 7% (99.64% confidence interval, 1%–14%, P=.001).

Discussion

There has been increasing emphasis on understanding and minimizing the rate of adverse events after surgical interventions such as ACDF. Prior work has identified overall associations of some complications with longer cases,13,14 with time having been considered a dichotomous variable.

A study by Gruskay et al13 found that ACDF operative time greater than the 75th percentile was associated with an increase in the risk for a “major complication” (odds ratio, 2.1). These findings were echoed by Schoenfeld et al,14 who found that surgical duration 1 SD above the mean for a variety of spinal arthrodesis procedures was associated with an increase in the rate of occurrence of 1 or more complications (odds ratio, 2.2).

As with other research, these 2 studies analyzed operative time using a Boolean approach, which is an appropriate means of testing for an association. However, a Boolean approach relies on 1 arbitrary cutoff point and does not account for the fact that an association may occur over the spectrum of operative times, not just near that cutoff. Moreover, it fails to quantify the increase in risk associated with a specific change in operative time over the spectrum of operative times.

Building on such prior studies, the current study evaluated the effect of incrementally longer operative times on general health outcomes after ACDF. Operative time was found to have a strong and independent association with adverse events and hospital metrics. Specifically, incremental increases in operative time were independently associated with increases in the occurrence of overall general health adverse events, extended hospital stay, and readmission, as well as venous thromboembolism, sepsis, and unplanned intubation. These increased risks represent the average increase in risk for patients, for 15-minute increases in surgical duration, across the spectrum of studied times. These findings are clinically applicable as strategies including defined orthopedic operating rooms and staff, decreased team substitutions, and the use of more efficient surgical techniques can all lead to incremental decreases in operative times.21–23

The association of the individual and overall adverse outcomes identified is consistent with the literature.13,14 The correlation of operative time with venous thromboembolism (deep venous thrombosis and/or pulmonary embolism) may be understood as sequelae of longer immobility during surgery.16,24 The association of operative time with an increased risk of sepsis may be related to patients undergoing longer surgeries being at increased risk for source infections. For example, longer retraction times can increase local tissue trauma and necrosis, leading to a potential infection source.25 Additionally, longer surgeries may be accompanied by longer durations of impaired thermal regulation, which have been associated with complications in elective spine surgeries.26–29

The association of operative time with unplanned intubation is likely multifactorial. Although the occurrence of other complications (eg, sepsis, venous thromboembolism) may contribute to this, it is most likely associated with increased edema related to the anterior cervical approach, which is known to be a greater factor in longer cases.30–33

In addition to adverse events, this study identified associations between increased surgical duration and both extended hospital stay and hospital readmission. The data suggested that an increase in surgical length by 15 minutes led to a 14% increase in risk for extended hospital stay and a 7% increase in risk for hospital readmission. Gruskay et al13 found that operative time in the 75th percentile (>171 minutes) was associated with an increased length of stay by approximately 0.7 days. Again, although aligning the 2 studies is imprecise because of their differing methodologies, the 2 studies are certainly consistent.

To the authors' knowledge, the current study is the first to independently examine and identify the relationship between increased operative time and the risk of hospital readmission. Notably, Lovecchio et al17 examined factors predicting readmission in 2261 patients undergoing ACDF or anterior corpectomy and fusion procedures. They could not identify a statistically significant relationship between operative time and hospital readmission.

The findings of this study are clinically compelling, as the increased risk for adverse events and hospital metrics are all associated with just a 15-minute increase in operative time. Interestingly, a variety of strategies have been studied and shown to improve operative time efficiency in the range of this magnitude. Small et al21 reported that dedicated orthopedic operating rooms and staff decreases operative time by 7 minutes following total joint arthroplasty. Cassera et al22 found that an increase in the number of team members involved in surgery by 1 individual, through mechanisms such as staff substitutions, led to an average lengthening of procedure time by 15 minutes for a variety of laparoscopic procedures. Additionally, technical modifications with a procedure can be associated with decreases in operative time. For example, the use of minimally invasive iliac crest bone harvesting has been shown to decrease operative time by 9 minutes compared with the traditional open window technique.23

Limitations of this study are those of the NSQIP. The program does not capture information on patient symptoms or radiographic findings. Additionally, the NSQIP does not assemble data regarding procedure-specific complications such as postoperative dysphagia, which has additionally been shown to be associated with operative time.34 This limits the analysis to nonspecific, general medical and surgical complications. Certainly not all ACDF procedures are of the same complexity, and greater surgical complexity may have been a confounder for extended operative time that could not be controlled. Nonetheless, restricting the analysis to 1-level procedures and excluding traumatic, oncologic, and infectious indications was done to limit the variability of cases studied. Furthermore, in comparison with nonparticipating hospitals, a larger percentage of NSQIP institutions are academic centers.35 Although impossible to completely account for this, the current study controlled for varying patient populations by including age, sex, body mass index, and the presence/absence of 8 comorbidities in all regressions. Finally, as with all data sets, the accuracy of the database is a potential source of error. However, the NSQIP undergoes routine quality audits and is thought to be of significantly greater data quality than administratively coded databases.15

Conclusion

This study used rigorous methodology to reveal and quantify independent associations between operative duration and several specific postoperative complications. The interval variable approach to analyzing operative time presents major advantages, has not been used previously in the spinal literature, and provides convincing evidence that incremental increases in operative duration independently modulate the risk for several specific adverse events following ACDF. Based on these data, efforts should be made by hospitals and surgeons alike to minimize the duration of surgical interventions.

References

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Patient Demographics

CharacteristicNo. (%)
Total15,241 (100.0)
Age
  18–49 y6593 (43.3)
  50–59 y4717 (30.9)
  60–69 y2699 (17.7)
  ≥70 y1232 (8.1)
Sex
  Male7589 (49.8)
  Female7652 (50.2)
Body mass index
  ≤24 kg/m23262 (21.4)
  25–29 kg/m25177 (34.0)
  ≥30 kg/m26802 (44.6)
Functional status
  Independent15,005 (98.5)
  Dependent236 (1.5)
Diabetic status
  No diabetes13,289 (87.2)
  Non–insulin-dependent diabetes mellitus1241 (8.1)
  Insulin-dependent diabetes mellitus711 (4.7)
Dyspnea on exertion748 (4.9)
Hypertension6224 (40.8)
Chronic obstructive pulmonary disease520 (3.4)
Anemia1487 (9.8)
Current smoker4500 (29.5)
American Society of Anesthesiologists class
  1815 (5.3)
  28980 (58.9)
  35225 (34.3)
  4221 (1.5)

Adverse Event and Hospital Metric Rates (N=15,241)

Adverse OutcomeNo. (%)
Any adverse event276 (1.81)
  Mortality9 (0.06)
  Myocardial infarction12 (0.08)
  Anemia requiring transfusion17 (0.11)
  Unplanned intubation63 (0.41)
  Pneumonia51 (0.33)
  Urinary tract infection67 (0.44)
  Surgical site infection66 (0.43)
  Sepsis5 (0.03)
  Wound dehiscence6 (0.04)
  Venous thromboembolism42 (0.28)
Adverse hospital metric
  Extended hospital stay (>1 day)3258 (21.38)
  Hospital readmission309 (2.03)

Impact of Operative Time on Risk for Adverse Outcomes

Adverse OutcomeImpact of a 15-Minute Increase in Operative Time on Risk for Adverse Outcomes

Relative Risk99.64% Confidence IntervalP
Any adverse event1.101.03–1.17<.001a
  Mortality0.950.69–1.32.652
  Myocardial infarction0.980.74–1.29.798
  Anemia requiring transfusion1.060.83–1.36.492
  Unplanned intubation1.171.03–1.33<.001a
  Pneumonia1.140.98–1.32.011
  Urinary tract infection1.030.90–1.18.508
  Surgical site infection1.100.97–1.25.032
  Sepsis1.441.03–2.03.002a
  Wound dehiscence0.950.71–1.26.591
  Venous thromboembolism1.191.04–1.37<.001a
Adverse hospital metric
  Extended hospital stay (>1 day)1.141.12–1.16<.001a
  Hospital readmission1.071.01–1.14.001a
Authors

The authors are from the Department of Orthopaedics and Rehabilitation (NTO, RPM, JJC, PB, JNG), Yale School of Medicine, New Haven, Connecticut; and the Department of Orthopaedic Surgery (DDB, KS), Rush University Medical Center, Chicago, Illinois.

Mr Ondeck, Dr Bohl, Mr McLynn, Mr Cui, and Mr Bovonratwet have no relevant financial relationships to disclose. Dr Singh is a paid consultant for Zimmer, Stryker, Pioneer, and DePuy; has received a grant from the Cervical Spine Research Society; receives royalties from Zimmer, Stryker, Pioneer, and DePuy; and holds stock in Avaz Surgical, LLC and Vital 5, LLC. Dr Grauer was previously a consultant for Adante Medical Devices, Isto Technologies, Vertex, Medtronic, Bioventus, and Stryker; has received a grant from the Orthopaedic Trauma Association; and is a clinical trial subinvestigator for Pfizer, Spinal Kinetics, and Orthofix.

Correspondence should be addressed to: Jonathan N. Grauer, MD, Department of Orthopaedics and Rehabilitation, Yale School of Medicine, 800 Howard Ave, New Haven, CT 06510 ( jonathan.grauer@yale.edu).

Received: July 03, 2017
Accepted: February 05, 2018

10.3928/01477447-20180424-02

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